Page 72 - UK Regulation Part 21 Initial Airworthiness Annex I (consolidated) March 2022

PART 21 - INITIAL AIRWORTHINESS (ANNEX I)

compliant with the latest certification specifications.
F.2.4 A description of the design feature and its intended function.
F.2.5 Data for the product pertinent to the requirement.
F.2.5.1 Service experience from such data sources, such as:
- Accident reports,
- Incident reports,
- Service bulletins,
- Airworthiness directives,
- Repairs,
- Modifications,
- Flight hours/cycles for fleet leader and total fleet,
- World airline accident summary data,
- Service difficulty reports,
- Accident Investigation Board reports, and
- Warranty, repair, and parts usage data.
F.2.5.2 Show that the data presented represent all relevant service experience for the
product, including the results of any operator surveys, and is comprehensive
enough to be representative.
F.2.5.3 Show that the service experience is relevant to the hazard.
F.2.5.4 Identification and evaluation of each of the main areas of concern with regard
to:
- Recurring and/or common failure modes,
- Cause,
- Probability by qualitative reasoning, and
- Measures already taken and their effects.
F.2.5.5 Relevant data pertaining to aircraft of similar design and construction may be
included.
F.2.5.6 Evaluation of failure modes and consequences through analytical processes.
The analytical processes should be supported by:
- A review of previous test results,
- Additional detailed testing as required, or
- A review of aircraft functional hazard assessments (FHA) and any
applicable system safety assessments (SSA) as required.
F.2.6 A conclusion that draws together the data and the rationale.
F.2.7 These guidelines are not intended to be limiting, either in setting the required
minimum elements or in precluding alternative forms of submission. Each case
may be different, based on the particulars of the system being examined and the
requirement to be addressed.
F .3 Example: 25.1141(f) for Transport Category Aeroplanes.
NOTE: This example is taken from the FAA’s certification experience, so references to
FAR sections and amendments are kept.
F.3.1 The following example, for transport category aeroplanes (§ 25.1141(f), APU Fuel
Valve Position Indication System), illustrates the typical process an applicant
follows. The process will be the same for all product types.
F.3.2 This example comes from a derived model transport aeroplane where significant
changes were made to the main airframe components, engines and systems, and
APU. The baseline aeroplane has an extensive service history. The example shows
how the use of service experience supports a finding that compliance with the latest
certification specifications would not contribute materially to the level of safety and
that application of the existing certification basis (or earlier amendment) would be
appropriate. The example is for significant derived models of transport aeroplanes
with extensive service history. It illustrates the process, following the guidelines in
this Appendix, but does not include the level of detail normally required.
F.3.2.1 Determine the differences between the certification specifications applied in
the original certification basis and the latest certification specification, and the
effect of the change to the certification specifications. The original certification
basis of the aeroplane that is being changed is the initial release of Part 25.
Amendment 25-40 added requirement § 25.1141(f), which mandates that
power-assisted valves must have a means to indicate to the flight crew when
the valve is in the fully open or closed position, or is moving between these
positions. The addressed hazard would be risk of APU fire due to fuel
accumulation caused by excessive unsuccessful APU start attempts.
F.3.2.2 What aspect of the proposed changed product would not meet the latest
certification specifications? The proposed APU fuel valve position indication
system does not provide the flight crew with fuel valve position or transition
indication and, therefore, does not comply with the requirements of §
25.1141(f).
F.3.2.3 The applicant provides evidence that the proposed certification basis for the
changed product, together with applicable service experience of the existing
design, provide a level of safety that approaches, yet is not fully compliant
with, the latest certification specifications. The APU fuel shut-off valve and
actuator are unchanged from those used on the current family of aeroplanes,
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